Conventional rubber compositions for automobile tires include those containing a conjugated diene polymer such as polybutadiene or butadiene-styrene copolymer and filler such as carbon black or silica.
Recent growing concern for environmental issues has increased the demand for automobiles with improved fuel economy. Thus, there is another need for rubber compositions for automobile tires that give excellent fuel economy.
One way that has been employed to improve fuel economy is to reduce the filler content. However, the rubber compositions prepared in this way have lower hardness and lower breaking properties, and also tend to have reduced wet grip performance.
Meanwhile, a typical way that has been employed to improve wet grip performance is to increase the filler content. Since wet grip performance has a trade-off relationship with fuel economy, it has been difficult to achieve a balanced improvement of these properties.
A number of attempts to improve wet grip performance have also been disclosed in which a special filler such as aluminum hydroxide is used with a common filler such as carbon black or silica (see Patent Literature 1, for example). However, such a method unfortunately deteriorates abrasion resistance and has room for improvement in the balance between wet grip performance and abrasion resistance.
Thus, the development of a technique for ensuring fuel economy while simultaneously maintaining wet grip performance and breaking properties has been desired.